Most of the current processes for producing polyolefins are co-current in nature and require a highly concentrated and purified olefin feedstock, which results in increased complexity and cost for polyolefin production. As the catalyst and olefin streams proceed through a series of reactors, increasingly dilute olefin is contacted with increasingly less active catalyst. As a consequence, incomplete conversion of the olefin is achievable in a single pass through the reactor. The unconverted olefin must be recycled to the beginning of the process. Unless a portion of this recycled stream is purged, the concentration of diluents in the polymerization reactors builds to unacceptable levels. In many current polymerization processes, the amount of purge ultimately is determined by the content of diluents in the fresh feed. High diluent concentrations in the feed demand high purge rates and concomitant olefin loss. In order to avoid such loss, extensive and complex separation schemes are required, which greatly increase the complexity, investment, and operational cost while reducing the reliability of the polymerization process.
An effective, efficient process is needed for handling dilute olefin feeds.